TOMOYO Linux Cross Reference
Linux/kernel/time/timer.c

   // SPDX-License-Identifier: GPL-2.0
   /*
    *  Kernel internal timers
    *
    *  Copyright (C) 1991, 1992  Linus Torvalds
    *
    *  1997-01-28  Modified by Finn Arne Gangstad to make timers scale better.
    *
    *  1997-09-10  Updated NTP code according to technical memorandum Jan '96
   *              "A Kernel Model for Precision Timekeeping" by Dave Mills
   *  1998-12-24  Fixed a xtime SMP race (we need the xtime_lock rw spinlock to
   *              serialize accesses to xtime/lost_ticks).
   *                              Copyright (C) 1998  Andrea Arcangeli
   *  1999-03-10  Improved NTP compatibility by Ulrich Windl
   *  2002-05-31  Move sys_sysinfo here and make its locking sane, Robert Love
   *  2000-10-05  Implemented scalable SMP per-CPU timer handling.
   *                              Copyright (C) 2000, 2001, 2002  Ingo Molnar
   *              Designed by David S. Miller, Alexey Kuznetsov and Ingo Molnar
   */
  
  #include <linux/kernel_stat.h>
  #include <linux/export.h>
  #include <linux/interrupt.h>
  #include <linux/percpu.h>
  #include <linux/init.h>
  #include <linux/mm.h>
  #include <linux/swap.h>
  #include <linux/pid_namespace.h>
  #include <linux/notifier.h>
  #include <linux/thread_info.h>
  #include <linux/time.h>
  #include <linux/jiffies.h>
  #include <linux/posix-timers.h>
  #include <linux/cpu.h>
  #include <linux/syscalls.h>
  #include <linux/delay.h>
  #include <linux/tick.h>
  #include <linux/kallsyms.h>
  #include <linux/irq_work.h>
  #include <linux/sched/signal.h>
  #include <linux/sched/sysctl.h>
  #include <linux/sched/nohz.h>
  #include <linux/sched/debug.h>
  #include <linux/slab.h>
  #include <linux/compat.h>
  #include <linux/random.h>
  #include <linux/sysctl.h>
  
  #include <linux/uaccess.h>
  #include <asm/unistd.h>
  #include <asm/div64.h>
  #include <asm/timex.h>
  #include <asm/io.h>
  
  #include "tick-internal.h"
  #include "timer_migration.h"
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/timer.h>
  
  __visible u64 jiffies_64 __cacheline_aligned_in_smp = INITIAL_JIFFIES;
  
  EXPORT_SYMBOL(jiffies_64);
  
  /*
   * The timer wheel has LVL_DEPTH array levels. Each level provides an array of
   * LVL_SIZE buckets. Each level is driven by its own clock and therefore each
   * level has a different granularity.
   *
   * The level granularity is:            LVL_CLK_DIV ^ level
   * The level clock frequency is:        HZ / (LVL_CLK_DIV ^ level)
   *
   * The array level of a newly armed timer depends on the relative expiry
   * time. The farther the expiry time is away the higher the array level and
   * therefore the granularity becomes.
   *
   * Contrary to the original timer wheel implementation, which aims for 'exact'
   * expiry of the timers, this implementation removes the need for recascading
   * the timers into the lower array levels. The previous 'classic' timer wheel
   * implementation of the kernel already violated the 'exact' expiry by adding
   * slack to the expiry time to provide batched expiration. The granularity
   * levels provide implicit batching.
   *
   * This is an optimization of the original timer wheel implementation for the
   * majority of the timer wheel use cases: timeouts. The vast majority of
   * timeout timers (networking, disk I/O ...) are canceled before expiry. If
   * the timeout expires it indicates that normal operation is disturbed, so it
   * does not matter much whether the timeout comes with a slight delay.
   *
   * The only exception to this are networking timers with a small expiry
   * time. They rely on the granularity. Those fit into the first wheel level,
   * which has HZ granularity.
   *
   * We don't have cascading anymore. timers with a expiry time above the
   * capacity of the last wheel level are force expired at the maximum timeout
   * value of the last wheel level. From data sampling we know that the maximum
   * value observed is 5 days (network connection tracking), so this should not
   * be an issue.
   *
  * The currently chosen array constants values are a good compromise between
  * array size and granularity.
  *
  * This results in the following granularity and range levels:
  *
  * HZ 1000 steps
  * Level Offset  Granularity            Range
  *  0      0         1 ms                0 ms -         63 ms
  *  1     64         8 ms               64 ms -        511 ms
  *  2    128        64 ms              512 ms -       4095 ms (512ms - ~4s)
  *  3    192       512 ms             4096 ms -      32767 ms (~4s - ~32s)
  *  4    256      4096 ms (~4s)      32768 ms -     262143 ms (~32s - ~4m)
  *  5    320     32768 ms (~32s)    262144 ms -    2097151 ms (~4m - ~34m)
  *  6    384    262144 ms (~4m)    2097152 ms -   16777215 ms (~34m - ~4h)
  *  7    448   2097152 ms (~34m)  16777216 ms -  134217727 ms (~4h - ~1d)
  *  8    512  16777216 ms (~4h)  134217728 ms - 1073741822 ms (~1d - ~12d)
  *
  * HZ  300
  * Level Offset  Granularity            Range
  *  0      0         3 ms                0 ms -        210 ms
  *  1     64        26 ms              213 ms -       1703 ms (213ms - ~1s)
  *  2    128       213 ms             1706 ms -      13650 ms (~1s - ~13s)
  *  3    192      1706 ms (~1s)      13653 ms -     109223 ms (~13s - ~1m)
  *  4    256     13653 ms (~13s)    109226 ms -     873810 ms (~1m - ~14m)
  *  5    320    109226 ms (~1m)     873813 ms -    6990503 ms (~14m - ~1h)
  *  6    384    873813 ms (~14m)   6990506 ms -   55924050 ms (~1h - ~15h)
  *  7    448   6990506 ms (~1h)   55924053 ms -  447392423 ms (~15h - ~5d)
  *  8    512  55924053 ms (~15h) 447392426 ms - 3579139406 ms (~5d - ~41d)
  *
  * HZ  250
  * Level Offset  Granularity            Range
  *  0      0         4 ms                0 ms -        255 ms
  *  1     64        32 ms              256 ms -       2047 ms (256ms - ~2s)
  *  2    128       256 ms             2048 ms -      16383 ms (~2s - ~16s)
  *  3    192      2048 ms (~2s)      16384 ms -     131071 ms (~16s - ~2m)
  *  4    256     16384 ms (~16s)    131072 ms -    1048575 ms (~2m - ~17m)
  *  5    320    131072 ms (~2m)    1048576 ms -    8388607 ms (~17m - ~2h)
  *  6    384   1048576 ms (~17m)   8388608 ms -   67108863 ms (~2h - ~18h)
  *  7    448   8388608 ms (~2h)   67108864 ms -  536870911 ms (~18h - ~6d)
  *  8    512  67108864 ms (~18h) 536870912 ms - 4294967288 ms (~6d - ~49d)
  *
  * HZ  100
  * Level Offset  Granularity            Range
  *  0      0         10 ms               0 ms -        630 ms
  *  1     64         80 ms             640 ms -       5110 ms (640ms - ~5s)
  *  2    128        640 ms            5120 ms -      40950 ms (~5s - ~40s)
  *  3    192       5120 ms (~5s)     40960 ms -     327670 ms (~40s - ~5m)
  *  4    256      40960 ms (~40s)   327680 ms -    2621430 ms (~5m - ~43m)
  *  5    320     327680 ms (~5m)   2621440 ms -   20971510 ms (~43m - ~5h)
  *  6    384    2621440 ms (~43m) 20971520 ms -  167772150 ms (~5h - ~1d)
  *  7    448   20971520 ms (~5h) 167772160 ms - 1342177270 ms (~1d - ~15d)
  */
 
 /* Clock divisor for the next level */
 #define LVL_CLK_SHIFT   3
 #define LVL_CLK_DIV     (1UL << LVL_CLK_SHIFT)
 #define LVL_CLK_MASK    (LVL_CLK_DIV - 1)
 #define LVL_SHIFT(n)    ((n) * LVL_CLK_SHIFT)
 #define LVL_GRAN(n)     (1UL << LVL_SHIFT(n))
 
 /*
  * The time start value for each level to select the bucket at enqueue
  * time. We start from the last possible delta of the previous level
  * so that we can later add an extra LVL_GRAN(n) to n (see calc_index()).
  */
 #define LVL_START(n)    ((LVL_SIZE - 1) << (((n) - 1) * LVL_CLK_SHIFT))
 
 /* Size of each clock level */
 #define LVL_BITS        6
 #define LVL_SIZE        (1UL << LVL_BITS)
 #define LVL_MASK        (LVL_SIZE - 1)
 #define LVL_OFFS(n)     ((n) * LVL_SIZE)
 
 /* Level depth */
 #if HZ > 100
 # define LVL_DEPTH      9
 # else
 # define LVL_DEPTH      8
 #endif
 
 /* The cutoff (max. capacity of the wheel) */
 #define WHEEL_TIMEOUT_CUTOFF    (LVL_START(LVL_DEPTH))
 #define WHEEL_TIMEOUT_MAX       (WHEEL_TIMEOUT_CUTOFF - LVL_GRAN(LVL_DEPTH - 1))
 
 /*
  * The resulting wheel size. If NOHZ is configured we allocate two
  * wheels so we have a separate storage for the deferrable timers.
  */
 #define WHEEL_SIZE      (LVL_SIZE * LVL_DEPTH)
 
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * If multiple bases need to be locked, use the base ordering for lock
  * nesting, i.e. lowest number first.
  */
 # define NR_BASES       3
 # define BASE_LOCAL     0
 # define BASE_GLOBAL    1
 # define BASE_DEF       2
 #else
 # define NR_BASES       1
 # define BASE_LOCAL     0
 # define BASE_GLOBAL    0
 # define BASE_DEF       0
 #endif
 
 /**
  * struct timer_base - Per CPU timer base (number of base depends on config)
  * @lock:               Lock protecting the timer_base
  * @running_timer:      When expiring timers, the lock is dropped. To make
  *                      sure not to race against deleting/modifying a
  *                      currently running timer, the pointer is set to the
  *                      timer, which expires at the moment. If no timer is
  *                      running, the pointer is NULL.
  * @expiry_lock:        PREEMPT_RT only: Lock is taken in softirq around
  *                      timer expiry callback execution and when trying to
  *                      delete a running timer and it wasn't successful in
  *                      the first glance. It prevents priority inversion
  *                      when callback was preempted on a remote CPU and a
  *                      caller tries to delete the running timer. It also
  *                      prevents a life lock, when the task which tries to
  *                      delete a timer preempted the softirq thread which
  *                      is running the timer callback function.
  * @timer_waiters:      PREEMPT_RT only: Tells, if there is a waiter
  *                      waiting for the end of the timer callback function
  *                      execution.
  * @clk:                clock of the timer base; is updated before enqueue
  *                      of a timer; during expiry, it is 1 offset ahead of
  *                      jiffies to avoid endless requeuing to current
  *                      jiffies
  * @next_expiry:        expiry value of the first timer; it is updated when
  *                      finding the next timer and during enqueue; the
  *                      value is not valid, when next_expiry_recalc is set
  * @cpu:                Number of CPU the timer base belongs to
  * @next_expiry_recalc: States, whether a recalculation of next_expiry is
  *                      required. Value is set true, when a timer was
  *                      deleted.
  * @is_idle:            Is set, when timer_base is idle. It is triggered by NOHZ
  *                      code. This state is only used in standard
  *                      base. Deferrable timers, which are enqueued remotely
  *                      never wake up an idle CPU. So no matter of supporting it
  *                      for this base.
  * @timers_pending:     Is set, when a timer is pending in the base. It is only
  *                      reliable when next_expiry_recalc is not set.
  * @pending_map:        bitmap of the timer wheel; each bit reflects a
  *                      bucket of the wheel. When a bit is set, at least a
  *                      single timer is enqueued in the related bucket.
  * @vectors:            Array of lists; Each array member reflects a bucket
  *                      of the timer wheel. The list contains all timers
  *                      which are enqueued into a specific bucket.
  */
 struct timer_base {
         raw_spinlock_t          lock;
         struct timer_list       *running_timer;
 #ifdef CONFIG_PREEMPT_RT
         spinlock_t              expiry_lock;
         atomic_t                timer_waiters;
 #endif
         unsigned long           clk;
         unsigned long           next_expiry;
         unsigned int            cpu;
         bool                    next_expiry_recalc;
         bool                    is_idle;
         bool                    timers_pending;
         DECLARE_BITMAP(pending_map, WHEEL_SIZE);
         struct hlist_head       vectors[WHEEL_SIZE];
 } ____cacheline_aligned;
 
 static DEFINE_PER_CPU(struct timer_base, timer_bases[NR_BASES]);
 
 #ifdef CONFIG_NO_HZ_COMMON
 
 static DEFINE_STATIC_KEY_FALSE(timers_nohz_active);
 static DEFINE_MUTEX(timer_keys_mutex);
 
 static void timer_update_keys(struct work_struct *work);
 static DECLARE_WORK(timer_update_work, timer_update_keys);
 
 #ifdef CONFIG_SMP
 static unsigned int sysctl_timer_migration = 1;
 
 DEFINE_STATIC_KEY_FALSE(timers_migration_enabled);
 
 static void timers_update_migration(void)
 {
         if (sysctl_timer_migration && tick_nohz_active)
                 static_branch_enable(&timers_migration_enabled);
         else
                 static_branch_disable(&timers_migration_enabled);
 }
 
 #ifdef CONFIG_SYSCTL
 static int timer_migration_handler(const struct ctl_table *table, int write,
                             void *buffer, size_t *lenp, loff_t *ppos)
 {
         int ret;
 
         mutex_lock(&timer_keys_mutex);
         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
         if (!ret && write)
                 timers_update_migration();
         mutex_unlock(&timer_keys_mutex);
         return ret;
 }
 
 static struct ctl_table timer_sysctl[] = {
         {
                 .procname       = "timer_migration",
                 .data           = &sysctl_timer_migration,
                 .maxlen         = sizeof(unsigned int),
                 .mode           = 0644,
                 .proc_handler   = timer_migration_handler,
                 .extra1         = SYSCTL_ZERO,
                 .extra2         = SYSCTL_ONE,
         },
 };
 
 static int __init timer_sysctl_init(void)
 {
         register_sysctl("kernel", timer_sysctl);
         return 0;
 }
 device_initcall(timer_sysctl_init);
 #endif /* CONFIG_SYSCTL */
 #else /* CONFIG_SMP */
 static inline void timers_update_migration(void) { }
 #endif /* !CONFIG_SMP */
 
 static void timer_update_keys(struct work_struct *work)
 {
         mutex_lock(&timer_keys_mutex);
         timers_update_migration();
         static_branch_enable(&timers_nohz_active);
         mutex_unlock(&timer_keys_mutex);
 }
 
 void timers_update_nohz(void)
 {
         schedule_work(&timer_update_work);
 }
 
 static inline bool is_timers_nohz_active(void)
 {
         return static_branch_unlikely(&timers_nohz_active);
 }
 #else
 static inline bool is_timers_nohz_active(void) { return false; }
 #endif /* NO_HZ_COMMON */
 
 static unsigned long round_jiffies_common(unsigned long j, int cpu,
                 bool force_up)
 {
         int rem;
         unsigned long original = j;
 
         /*
          * We don't want all cpus firing their timers at once hitting the
          * same lock or cachelines, so we skew each extra cpu with an extra
          * 3 jiffies. This 3 jiffies came originally from the mm/ code which
          * already did this.
          * The skew is done by adding 3*cpunr, then round, then subtract this
          * extra offset again.
          */
         j += cpu * 3;
 
         rem = j % HZ;
 
         /*
          * If the target jiffie is just after a whole second (which can happen
          * due to delays of the timer irq, long irq off times etc etc) then
          * we should round down to the whole second, not up. Use 1/4th second
          * as cutoff for this rounding as an extreme upper bound for this.
          * But never round down if @force_up is set.
          */
         if (rem < HZ/4 && !force_up) /* round down */
                 j = j - rem;
         else /* round up */
                 j = j - rem + HZ;
 
         /* now that we have rounded, subtract the extra skew again */
         j -= cpu * 3;
 
         /*
          * Make sure j is still in the future. Otherwise return the
          * unmodified value.
          */
         return time_is_after_jiffies(j) ? j : original;
 }
 
 /**
  * __round_jiffies - function to round jiffies to a full second
  * @j: the time in (absolute) jiffies that should be rounded
  * @cpu: the processor number on which the timeout will happen
  *
  * __round_jiffies() rounds an absolute time in the future (in jiffies)
  * up or down to (approximately) full seconds. This is useful for timers
  * for which the exact time they fire does not matter too much, as long as
  * they fire approximately every X seconds.
  *
  * By rounding these timers to whole seconds, all such timers will fire
  * at the same time, rather than at various times spread out. The goal
  * of this is to have the CPU wake up less, which saves power.
  *
  * The exact rounding is skewed for each processor to avoid all
  * processors firing at the exact same time, which could lead
  * to lock contention or spurious cache line bouncing.
  *
  * The return value is the rounded version of the @j parameter.
  */
 unsigned long __round_jiffies(unsigned long j, int cpu)
 {
         return round_jiffies_common(j, cpu, false);
 }
 EXPORT_SYMBOL_GPL(__round_jiffies);
 
 /**
  * __round_jiffies_relative - function to round jiffies to a full second
  * @j: the time in (relative) jiffies that should be rounded
  * @cpu: the processor number on which the timeout will happen
  *
  * __round_jiffies_relative() rounds a time delta  in the future (in jiffies)
  * up or down to (approximately) full seconds. This is useful for timers
  * for which the exact time they fire does not matter too much, as long as
  * they fire approximately every X seconds.
  *
  * By rounding these timers to whole seconds, all such timers will fire
  * at the same time, rather than at various times spread out. The goal
  * of this is to have the CPU wake up less, which saves power.
  *
  * The exact rounding is skewed for each processor to avoid all
  * processors firing at the exact same time, which could lead
  * to lock contention or spurious cache line bouncing.
  *
  * The return value is the rounded version of the @j parameter.
  */
 unsigned long __round_jiffies_relative(unsigned long j, int cpu)
 {
         unsigned long j0 = jiffies;
 
         /* Use j0 because jiffies might change while we run */
         return round_jiffies_common(j + j0, cpu, false) - j0;
 }
 EXPORT_SYMBOL_GPL(__round_jiffies_relative);
 
 /**
  * round_jiffies - function to round jiffies to a full second
  * @j: the time in (absolute) jiffies that should be rounded
  *
  * round_jiffies() rounds an absolute time in the future (in jiffies)
  * up or down to (approximately) full seconds. This is useful for timers
  * for which the exact time they fire does not matter too much, as long as
  * they fire approximately every X seconds.
  *
  * By rounding these timers to whole seconds, all such timers will fire
  * at the same time, rather than at various times spread out. The goal
  * of this is to have the CPU wake up less, which saves power.
  *
  * The return value is the rounded version of the @j parameter.
  */
 unsigned long round_jiffies(unsigned long j)
 {
         return round_jiffies_common(j, raw_smp_processor_id(), false);
 }
 EXPORT_SYMBOL_GPL(round_jiffies);
 
 /**
  * round_jiffies_relative - function to round jiffies to a full second
  * @j: the time in (relative) jiffies that should be rounded
  *
  * round_jiffies_relative() rounds a time delta  in the future (in jiffies)
  * up or down to (approximately) full seconds. This is useful for timers
  * for which the exact time they fire does not matter too much, as long as
  * they fire approximately every X seconds.
  *
  * By rounding these timers to whole seconds, all such timers will fire
  * at the same time, rather than at various times spread out. The goal
  * of this is to have the CPU wake up less, which saves power.
  *
  * The return value is the rounded version of the @j parameter.
  */
 unsigned long round_jiffies_relative(unsigned long j)
 {
         return __round_jiffies_relative(j, raw_smp_processor_id());
 }
 EXPORT_SYMBOL_GPL(round_jiffies_relative);
 
 /**
  * __round_jiffies_up - function to round jiffies up to a full second
  * @j: the time in (absolute) jiffies that should be rounded
  * @cpu: the processor number on which the timeout will happen
  *
  * This is the same as __round_jiffies() except that it will never
  * round down.  This is useful for timeouts for which the exact time
  * of firing does not matter too much, as long as they don't fire too
  * early.
  */
 unsigned long __round_jiffies_up(unsigned long j, int cpu)
 {
         return round_jiffies_common(j, cpu, true);
 }
 EXPORT_SYMBOL_GPL(__round_jiffies_up);
 
 /**
  * __round_jiffies_up_relative - function to round jiffies up to a full second
  * @j: the time in (relative) jiffies that should be rounded
  * @cpu: the processor number on which the timeout will happen
  *
  * This is the same as __round_jiffies_relative() except that it will never
  * round down.  This is useful for timeouts for which the exact time
  * of firing does not matter too much, as long as they don't fire too
  * early.
  */
 unsigned long __round_jiffies_up_relative(unsigned long j, int cpu)
 {
         unsigned long j0 = jiffies;
 
         /* Use j0 because jiffies might change while we run */
         return round_jiffies_common(j + j0, cpu, true) - j0;
 }
 EXPORT_SYMBOL_GPL(__round_jiffies_up_relative);
 
 /**
  * round_jiffies_up - function to round jiffies up to a full second
  * @j: the time in (absolute) jiffies that should be rounded
  *
  * This is the same as round_jiffies() except that it will never
  * round down.  This is useful for timeouts for which the exact time
  * of firing does not matter too much, as long as they don't fire too
  * early.
  */
 unsigned long round_jiffies_up(unsigned long j)
 {
         return round_jiffies_common(j, raw_smp_processor_id(), true);
 }
 EXPORT_SYMBOL_GPL(round_jiffies_up);
 
 /**
  * round_jiffies_up_relative - function to round jiffies up to a full second
  * @j: the time in (relative) jiffies that should be rounded
  *
  * This is the same as round_jiffies_relative() except that it will never
  * round down.  This is useful for timeouts for which the exact time
  * of firing does not matter too much, as long as they don't fire too
  * early.
  */
 unsigned long round_jiffies_up_relative(unsigned long j)
 {
         return __round_jiffies_up_relative(j, raw_smp_processor_id());
 }
 EXPORT_SYMBOL_GPL(round_jiffies_up_relative);
 
 
 static inline unsigned int timer_get_idx(struct timer_list *timer)
 {
         return (timer->flags & TIMER_ARRAYMASK) >> TIMER_ARRAYSHIFT;
 }
 
 static inline void timer_set_idx(struct timer_list *timer, unsigned int idx)
 {
         timer->flags = (timer->flags & ~TIMER_ARRAYMASK) |
                         idx << TIMER_ARRAYSHIFT;
 }
 
 /*
  * Helper function to calculate the array index for a given expiry
  * time.
  */
 static inline unsigned calc_index(unsigned long expires, unsigned lvl,
                                   unsigned long *bucket_expiry)
 {
 
         /*
          * The timer wheel has to guarantee that a timer does not fire
          * early. Early expiry can happen due to:
          * - Timer is armed at the edge of a tick
          * - Truncation of the expiry time in the outer wheel levels
          *
          * Round up with level granularity to prevent this.
          */
         expires = (expires >> LVL_SHIFT(lvl)) + 1;
         *bucket_expiry = expires << LVL_SHIFT(lvl);
         return LVL_OFFS(lvl) + (expires & LVL_MASK);
 }
 
 static int calc_wheel_index(unsigned long expires, unsigned long clk,
                             unsigned long *bucket_expiry)
 {
         unsigned long delta = expires - clk;
         unsigned int idx;
 
         if (delta < LVL_START(1)) {
                 idx = calc_index(expires, 0, bucket_expiry);
         } else if (delta < LVL_START(2)) {
                 idx = calc_index(expires, 1, bucket_expiry);
         } else if (delta < LVL_START(3)) {
                 idx = calc_index(expires, 2, bucket_expiry);
         } else if (delta < LVL_START(4)) {
                 idx = calc_index(expires, 3, bucket_expiry);
         } else if (delta < LVL_START(5)) {
                 idx = calc_index(expires, 4, bucket_expiry);
         } else if (delta < LVL_START(6)) {
                 idx = calc_index(expires, 5, bucket_expiry);
         } else if (delta < LVL_START(7)) {
                 idx = calc_index(expires, 6, bucket_expiry);
         } else if (LVL_DEPTH > 8 && delta < LVL_START(8)) {
                 idx = calc_index(expires, 7, bucket_expiry);
         } else if ((long) delta < 0) {
                 idx = clk & LVL_MASK;
                 *bucket_expiry = clk;
         } else {
                 /*
                  * Force expire obscene large timeouts to expire at the
                  * capacity limit of the wheel.
                  */
                 if (delta >= WHEEL_TIMEOUT_CUTOFF)
                         expires = clk + WHEEL_TIMEOUT_MAX;
 
                 idx = calc_index(expires, LVL_DEPTH - 1, bucket_expiry);
         }
         return idx;
 }
 
 static void
 trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
 {
         /*
          * Deferrable timers do not prevent the CPU from entering dynticks and
          * are not taken into account on the idle/nohz_full path. An IPI when a
          * new deferrable timer is enqueued will wake up the remote CPU but
          * nothing will be done with the deferrable timer base. Therefore skip
          * the remote IPI for deferrable timers completely.
          */
         if (!is_timers_nohz_active() || timer->flags & TIMER_DEFERRABLE)
                 return;
 
         /*
          * We might have to IPI the remote CPU if the base is idle and the
          * timer is pinned. If it is a non pinned timer, it is only queued
          * on the remote CPU, when timer was running during queueing. Then
          * everything is handled by remote CPU anyway. If the other CPU is
          * on the way to idle then it can't set base->is_idle as we hold
          * the base lock:
          */
         if (base->is_idle) {
                 WARN_ON_ONCE(!(timer->flags & TIMER_PINNED ||
                                tick_nohz_full_cpu(base->cpu)));
                 wake_up_nohz_cpu(base->cpu);
         }
 }
 
 /*
  * Enqueue the timer into the hash bucket, mark it pending in
  * the bitmap, store the index in the timer flags then wake up
  * the target CPU if needed.
  */
 static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
                           unsigned int idx, unsigned long bucket_expiry)
 {
 
         hlist_add_head(&timer->entry, base->vectors + idx);
         __set_bit(idx, base->pending_map);
         timer_set_idx(timer, idx);
 
         trace_timer_start(timer, bucket_expiry);
 
         /*
          * Check whether this is the new first expiring timer. The
          * effective expiry time of the timer is required here
          * (bucket_expiry) instead of timer->expires.
          */
         if (time_before(bucket_expiry, base->next_expiry)) {
                 /*
                  * Set the next expiry time and kick the CPU so it
                  * can reevaluate the wheel:
                  */
                 base->next_expiry = bucket_expiry;
                 base->timers_pending = true;
                 base->next_expiry_recalc = false;
                 trigger_dyntick_cpu(base, timer);
         }
 }
 
 static void internal_add_timer(struct timer_base *base, struct timer_list *timer)
 {
         unsigned long bucket_expiry;
         unsigned int idx;
 
         idx = calc_wheel_index(timer->expires, base->clk, &bucket_expiry);
         enqueue_timer(base, timer, idx, bucket_expiry);
 }
 
 #ifdef CONFIG_DEBUG_OBJECTS_TIMERS
 
 static const struct debug_obj_descr timer_debug_descr;
 
 struct timer_hint {
         void    (*function)(struct timer_list *t);
         long    offset;
 };
 
 #define TIMER_HINT(fn, container, timr, hintfn)                 \
         {                                                       \
                 .function = fn,                                 \
                 .offset   = offsetof(container, hintfn) -       \
                             offsetof(container, timr)           \
         }
 
 static const struct timer_hint timer_hints[] = {
         TIMER_HINT(delayed_work_timer_fn,
                    struct delayed_work, timer, work.func),
         TIMER_HINT(kthread_delayed_work_timer_fn,
                    struct kthread_delayed_work, timer, work.func),
 };
 
 static void *timer_debug_hint(void *addr)
 {
         struct timer_list *timer = addr;
         int i;
 
         for (i = 0; i < ARRAY_SIZE(timer_hints); i++) {
                 if (timer_hints[i].function == timer->function) {
                         void (**fn)(void) = addr + timer_hints[i].offset;
 
                         return *fn;
                 }
         }
 
         return timer->function;
 }
 
 static bool timer_is_static_object(void *addr)
 {
         struct timer_list *timer = addr;
 
         return (timer->entry.pprev == NULL &&
                 timer->entry.next == TIMER_ENTRY_STATIC);
 }
 
 /*
  * timer_fixup_init is called when:
  * - an active object is initialized
  */
 static bool timer_fixup_init(void *addr, enum debug_obj_state state)
 {
         struct timer_list *timer = addr;
 
         switch (state) {
         case ODEBUG_STATE_ACTIVE:
                 del_timer_sync(timer);
                 debug_object_init(timer, &timer_debug_descr);
                 return true;
         default:
                 return false;
         }
 }
 
 /* Stub timer callback for improperly used timers. */
 static void stub_timer(struct timer_list *unused)
 {
         WARN_ON(1);
 }
 
 /*
  * timer_fixup_activate is called when:
  * - an active object is activated
  * - an unknown non-static object is activated
  */
 static bool timer_fixup_activate(void *addr, enum debug_obj_state state)
 {
         struct timer_list *timer = addr;
 
         switch (state) {
         case ODEBUG_STATE_NOTAVAILABLE:
                 timer_setup(timer, stub_timer, 0);
                 return true;
 
         case ODEBUG_STATE_ACTIVE:
                 WARN_ON(1);
                 fallthrough;
         default:
                 return false;
         }
 }
 
 /*
  * timer_fixup_free is called when:
  * - an active object is freed
  */
 static bool timer_fixup_free(void *addr, enum debug_obj_state state)
 {
         struct timer_list *timer = addr;
 
         switch (state) {
         case ODEBUG_STATE_ACTIVE:
                 del_timer_sync(timer);
                 debug_object_free(timer, &timer_debug_descr);
                 return true;
         default:
                 return false;
         }
 }
 
 /*
  * timer_fixup_assert_init is called when:
  * - an untracked/uninit-ed object is found
  */
 static bool timer_fixup_assert_init(void *addr, enum debug_obj_state state)
 {
         struct timer_list *timer = addr;
 
         switch (state) {
         case ODEBUG_STATE_NOTAVAILABLE:
                 timer_setup(timer, stub_timer, 0);
                 return true;
         default:
                 return false;
         }
 }
 
 static const struct debug_obj_descr timer_debug_descr = {
         .name                   = "timer_list",
         .debug_hint             = timer_debug_hint,
         .is_static_object       = timer_is_static_object,
         .fixup_init             = timer_fixup_init,
         .fixup_activate         = timer_fixup_activate,
         .fixup_free             = timer_fixup_free,
         .fixup_assert_init      = timer_fixup_assert_init,
 };
 
 static inline void debug_timer_init(struct timer_list *timer)
 {
         debug_object_init(timer, &timer_debug_descr);
 }
 
 static inline void debug_timer_activate(struct timer_list *timer)
 {
         debug_object_activate(timer, &timer_debug_descr);
 }
 
 static inline void debug_timer_deactivate(struct timer_list *timer)
 {
         debug_object_deactivate(timer, &timer_debug_descr);
 }
 
 static inline void debug_timer_assert_init(struct timer_list *timer)
 {
         debug_object_assert_init(timer, &timer_debug_descr);
 }
 
 static void do_init_timer(struct timer_list *timer,
                           void (*func)(struct timer_list *),
                           unsigned int flags,
                           const char *name, struct lock_class_key *key);
 
 void init_timer_on_stack_key(struct timer_list *timer,
                              void (*func)(struct timer_list *),
                              unsigned int flags,
                              const char *name, struct lock_class_key *key)
 {
         debug_object_init_on_stack(timer, &timer_debug_descr);
         do_init_timer(timer, func, flags, name, key);
 }
 EXPORT_SYMBOL_GPL(init_timer_on_stack_key);
 
 void destroy_timer_on_stack(struct timer_list *timer)
 {
         debug_object_free(timer, &timer_debug_descr);
 }
 EXPORT_SYMBOL_GPL(destroy_timer_on_stack);
 
 #else
 static inline void debug_timer_init(struct timer_list *timer) { }
 static inline void debug_timer_activate(struct timer_list *timer) { }
 static inline void debug_timer_deactivate(struct timer_list *timer) { }
 static inline void debug_timer_assert_init(struct timer_list *timer) { }
 #endif
 
 static inline void debug_init(struct timer_list *timer)
 {
         debug_timer_init(timer);
         trace_timer_init(timer);
 }
 
 static inline void debug_deactivate(struct timer_list *timer)
 {
         debug_timer_deactivate(timer);
         trace_timer_cancel(timer);
 }
 
 static inline void debug_assert_init(struct timer_list *timer)
 {
         debug_timer_assert_init(timer);
 }
 
 static void do_init_timer(struct timer_list *timer,
                           void (*func)(struct timer_list *),
                           unsigned int flags,
                           const char *name, struct lock_class_key *key)
 {
         timer->entry.pprev = NULL;
         timer->function = func;
         if (WARN_ON_ONCE(flags & ~TIMER_INIT_FLAGS))
                 flags &= TIMER_INIT_FLAGS;
         timer->flags = flags | raw_smp_processor_id();
         lockdep_init_map(&timer->lockdep_map, name, key, 0);
 }
 
 /**
  * init_timer_key - initialize a timer
  * @timer: the timer to be initialized
  * @func: timer callback function
  * @flags: timer flags
  * @name: name of the timer
  * @key: lockdep class key of the fake lock used for tracking timer
  *       sync lock dependencies
  *
  * init_timer_key() must be done to a timer prior to calling *any* of the
  * other timer functions.
  */
 void init_timer_key(struct timer_list *timer,
                     void (*func)(struct timer_list *), unsigned int flags,
                     const char *name, struct lock_class_key *key)
 {
         debug_init(timer);
         do_init_timer(timer, func, flags, name, key);
 }
 EXPORT_SYMBOL(init_timer_key);
 
 static inline void detach_timer(struct timer_list *timer, bool clear_pending)
 {
         struct hlist_node *entry = &timer->entry;
 
         debug_deactivate(timer);
 
         __hlist_del(entry);
         if (clear_pending)
                 entry->pprev = NULL;
         entry->next = LIST_POISON2;
 }
 
 static int detach_if_pending(struct timer_list *timer, struct timer_base *base,
                              bool clear_pending)
 {
         unsigned idx = timer_get_idx(timer);
 
         if (!timer_pending(timer))
                 return 0;
 
         if (hlist_is_singular_node(&timer->entry, base->vectors + idx)) {
                 __clear_bit(idx, base->pending_map);
                 base->next_expiry_recalc = true;
         }
 
         detach_timer(timer, clear_pending);
         return 1;
 }
 
 static inline struct timer_base *get_timer_cpu_base(u32 tflags, u32 cpu)
 {
         int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
         struct timer_base *base;
 
         base = per_cpu_ptr(&timer_bases[index], cpu);
 
         /*
          * If the timer is deferrable and NO_HZ_COMMON is set then we need
          * to use the deferrable base.
          */
         if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
                 base = per_cpu_ptr(&timer_bases[BASE_DEF], cpu);
         return base;
 }
 
 static inline struct timer_base *get_timer_this_cpu_base(u32 tflags)
 {
         int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
         struct timer_base *base;
 
         base = this_cpu_ptr(&timer_bases[index]);
 
         /*
          * If the timer is deferrable and NO_HZ_COMMON is set then we need
          * to use the deferrable base.
          */
         if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
                 base = this_cpu_ptr(&timer_bases[BASE_DEF]);
         return base;
 }
 
 static inline struct timer_base *get_timer_base(u32 tflags)
 {
         return get_timer_cpu_base(tflags, tflags & TIMER_CPUMASK);
 }
 
 static inline void __forward_timer_base(struct timer_base *base,
                                         unsigned long basej)
 {
         /*
          * Check whether we can forward the base. We can only do that when
          * @basej is past base->clk otherwise we might rewind base->clk.
          */
         if (time_before_eq(basej, base->clk))
                 return;
 
         /*
          * If the next expiry value is > jiffies, then we fast forward to
          * jiffies otherwise we forward to the next expiry value.
          */
         if (time_after(base->next_expiry, basej)) {
                 base->clk = basej;
         } else {
                 if (WARN_ON_ONCE(time_before(base->next_expiry, base->clk)))
                         return;
                 base->clk = base->next_expiry;
         }
 
 }
 
 static inline void forward_timer_base(struct timer_base *base)
 {
         __forward_timer_base(base, READ_ONCE(jiffies));
 }
 
 /*
  * We are using hashed locking: Holding per_cpu(timer_bases[x]).lock means
  * that all timers which are tied to this base are locked, and the base itself
  * is locked too.
  *
  * So __run_timers/migrate_timers can safely modify all timers which could
  * be found in the base->vectors array.
  *
  * When a timer is migrating then the TIMER_MIGRATING flag is set and we need
  * to wait until the migration is done.
  */
 static struct timer_base *lock_timer_base(struct timer_list *timer,
                                           unsigned long *flags)
         __acquires(timer->base->lock)
 {
         for (;;) {
                 struct timer_base *base;
                 u32 tf;
 
                 /*
                  * We need to use READ_ONCE() here, otherwise the compiler
                  * might re-read @tf between the check for TIMER_MIGRATING
                  * and spin_lock().
                  */
                 tf = READ_ONCE(timer->flags);
 
                 if (!(tf & TIMER_MIGRATING)) {
                         base = get_timer_base(tf);
                         raw_spin_lock_irqsave(&base->lock, *flags);
                         if (timer->flags == tf)
                                 return base;
                         raw_spin_unlock_irqrestore(&base->lock, *flags);
                 }
                 cpu_relax();
         }
 }
 
 #define MOD_TIMER_PENDING_ONLY          0x01
 #define MOD_TIMER_REDUCE                0x02
 #define MOD_TIMER_NOTPENDING            0x04
 
 static inline int
 __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int options)
 {
         unsigned long clk = 0, flags, bucket_expiry;
         struct timer_base *base, *new_base;
         unsigned int idx = UINT_MAX;
         int ret = 0;
 
         debug_assert_init(timer);
 
         /*
          * This is a common optimization triggered by the networking code - if
          * the timer is re-modified to have the same timeout or ends up in the
          * same array bucket then just return:
          */
         if (!(options & MOD_TIMER_NOTPENDING) && timer_pending(timer)) {
                 /*
                  * The downside of this optimization is that it can result in
                  * larger granularity than you would get from adding a new
                  * timer with this expiry.
                  */
                 long diff = timer->expires - expires;
 
                 if (!diff)
                         return 1;
                 if (options & MOD_TIMER_REDUCE && diff <= 0)
                         return 1;
 
                 /*
                  * We lock timer base and calculate the bucket index right
                  * here. If the timer ends up in the same bucket, then we
                  * just update the expiry time and avoid the whole
                  * dequeue/enqueue dance.
                  */
                 base = lock_timer_base(timer, &flags);
                 /*
                  * Has @timer been shutdown? This needs to be evaluated
                  * while holding base lock to prevent a race against the
                  * shutdown code.
                  */
                 if (!timer->function)
                         goto out_unlock;
 
                 forward_timer_base(base);
 
                 if (timer_pending(timer) && (options & MOD_TIMER_REDUCE) &&
                     time_before_eq(timer->expires, expires)) {
                         ret = 1;
                         goto out_unlock;
                 }
 
                 clk = base->clk;
                 idx = calc_wheel_index(expires, clk, &bucket_expiry);
 
                 /*
                  * Retrieve and compare the array index of the pending
                  * timer. If it matches set the expiry to the new value so a
                  * subsequent call will exit in the expires check above.
                  */
                 if (idx == timer_get_idx(timer)) {
                         if (!(options & MOD_TIMER_REDUCE))
                                 timer->expires = expires;
                         else if (time_after(timer->expires, expires))
                                 timer->expires = expires;
                         ret = 1;
                         goto out_unlock;
                 }
         } else {
                 base = lock_timer_base(timer, &flags);
                 /*
                  * Has @timer been shutdown? This needs to be evaluated
                  * while holding base lock to prevent a race against the
                  * shutdown code.
                  */
                 if (!timer->function)
                         goto out_unlock;
 
                 forward_timer_base(base);
         }
 
         ret = detach_if_pending(timer, base, false);
         if (!ret && (options & MOD_TIMER_PENDING_ONLY))
                 goto out_unlock;
 
         new_base = get_timer_this_cpu_base(timer->flags);
 
         if (base != new_base) {
                 /*
                  * We are trying to schedule the timer on the new base.
                  * However we can't change timer's base while it is running,
                  * otherwise timer_delete_sync() can't detect that the timer's
                  * handler yet has not finished. This also guarantees that the
                  * timer is serialized wrt itself.
                  */
                 if (likely(base->running_timer != timer)) {
                         /* See the comment in lock_timer_base() */
                         timer->flags |= TIMER_MIGRATING;
 
                         raw_spin_unlock(&base->lock);
                         base = new_base;
                         raw_spin_lock(&base->lock);
                         WRITE_ONCE(timer->flags,
                                    (timer->flags & ~TIMER_BASEMASK) | base->cpu);
                         forward_timer_base(base);
                 }
         }
 
         debug_timer_activate(timer);
 
         timer->expires = expires;
         /*
          * If 'idx' was calculated above and the base time did not advance
          * between calculating 'idx' and possibly switching the base, only
          * enqueue_timer() is required. Otherwise we need to (re)calculate
          * the wheel index via internal_add_timer().
          */
         if (idx != UINT_MAX && clk == base->clk)
                 enqueue_timer(base, timer, idx, bucket_expiry);
         else
                 internal_add_timer(base, timer);
 
 out_unlock:
         raw_spin_unlock_irqrestore(&base->lock, flags);
 
         return ret;
 }
 
 /**
  * mod_timer_pending - Modify a pending timer's timeout
  * @timer:      The pending timer to be modified
  * @expires:    New absolute timeout in jiffies
  *
  * mod_timer_pending() is the same for pending timers as mod_timer(), but
  * will not activate inactive timers.
  *
  * If @timer->function == NULL then the start operation is silently
  * discarded.
  *
  * Return:
  * * %0 - The timer was inactive and not modified or was in
  *        shutdown state and the operation was discarded
  * * %1 - The timer was active and requeued to expire at @expires
  */
 int mod_timer_pending(struct timer_list *timer, unsigned long expires)
 {
         return __mod_timer(timer, expires, MOD_TIMER_PENDING_ONLY);
 }
 EXPORT_SYMBOL(mod_timer_pending);
 
 /**
  * mod_timer - Modify a timer's timeout
  * @timer:      The timer to be modified
  * @expires:    New absolute timeout in jiffies
  *
  * mod_timer(timer, expires) is equivalent to:
  *
  *     del_timer(timer); timer->expires = expires; add_timer(timer);
  *
  * mod_timer() is more efficient than the above open coded sequence. In
  * case that the timer is inactive, the del_timer() part is a NOP. The
  * timer is in any case activated with the new expiry time @expires.
  *
  * Note that if there are multiple unserialized concurrent users of the
  * same timer, then mod_timer() is the only safe way to modify the timeout,
  * since add_timer() cannot modify an already running timer.
  *
  * If @timer->function == NULL then the start operation is silently
  * discarded. In this case the return value is 0 and meaningless.
  *
  * Return:
  * * %0 - The timer was inactive and started or was in shutdown
  *        state and the operation was discarded
  * * %1 - The timer was active and requeued to expire at @expires or
  *        the timer was active and not modified because @expires did
  *        not change the effective expiry time
  */
 int mod_timer(struct timer_list *timer, unsigned long expires)
 {
         return __mod_timer(timer, expires, 0);
 }
 EXPORT_SYMBOL(mod_timer);
 
 /**
  * timer_reduce - Modify a timer's timeout if it would reduce the timeout
  * @timer:      The timer to be modified
  * @expires:    New absolute timeout in jiffies
  *
  * timer_reduce() is very similar to mod_timer(), except that it will only
  * modify an enqueued timer if that would reduce the expiration time. If
  * @timer is not enqueued it starts the timer.
  *
  * If @timer->function == NULL then the start operation is silently
  * discarded.
  *
  * Return:
  * * %0 - The timer was inactive and started or was in shutdown
  *        state and the operation was discarded
  * * %1 - The timer was active and requeued to expire at @expires or
  *        the timer was active and not modified because @expires
  *        did not change the effective expiry time such that the
  *        timer would expire earlier than already scheduled
  */
 int timer_reduce(struct timer_list *timer, unsigned long expires)
 {
         return __mod_timer(timer, expires, MOD_TIMER_REDUCE);
 }
 EXPORT_SYMBOL(timer_reduce);
 
 /**
  * add_timer - Start a timer
  * @timer:      The timer to be started
  *
  * Start @timer to expire at @timer->expires in the future. @timer->expires
  * is the absolute expiry time measured in 'jiffies'. When the timer expires
  * timer->function(timer) will be invoked from soft interrupt context.
  *
  * The @timer->expires and @timer->function fields must be set prior
  * to calling this function.
  *
  * If @timer->function == NULL then the start operation is silently
  * discarded.
  *
  * If @timer->expires is already in the past @timer will be queued to
  * expire at the next timer tick.
  *
  * This can only operate on an inactive timer. Attempts to invoke this on
  * an active timer are rejected with a warning.
  */
 void add_timer(struct timer_list *timer)
 {
         if (WARN_ON_ONCE(timer_pending(timer)))
                 return;
         __mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
 }
 EXPORT_SYMBOL(add_timer);
 
 /**
  * add_timer_local() - Start a timer on the local CPU
  * @timer:      The timer to be started
  *
  * Same as add_timer() except that the timer flag TIMER_PINNED is set.
  *
  * See add_timer() for further details.
  */
 void add_timer_local(struct timer_list *timer)
 {
         if (WARN_ON_ONCE(timer_pending(timer)))
                 return;
         timer->flags |= TIMER_PINNED;
         __mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
 }
 EXPORT_SYMBOL(add_timer_local);
 
 /**
  * add_timer_global() - Start a timer without TIMER_PINNED flag set
  * @timer:      The timer to be started
  *
  * Same as add_timer() except that the timer flag TIMER_PINNED is unset.
  *
  * See add_timer() for further details.
  */
 void add_timer_global(struct timer_list *timer)
 {
         if (WARN_ON_ONCE(timer_pending(timer)))
                 return;
         timer->flags &= ~TIMER_PINNED;
         __mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
 }
 EXPORT_SYMBOL(add_timer_global);
 
 /**
  * add_timer_on - Start a timer on a particular CPU
  * @timer:      The timer to be started
  * @cpu:        The CPU to start it on
  *
  * Same as add_timer() except that it starts the timer on the given CPU and
  * the TIMER_PINNED flag is set. When timer shouldn't be a pinned timer in
  * the next round, add_timer_global() should be used instead as it unsets
  * the TIMER_PINNED flag.
  *
  * See add_timer() for further details.
  */
 void add_timer_on(struct timer_list *timer, int cpu)
 {
         struct timer_base *new_base, *base;
         unsigned long flags;
 
         debug_assert_init(timer);
 
         if (WARN_ON_ONCE(timer_pending(timer)))
                 return;
 
         /* Make sure timer flags have TIMER_PINNED flag set */
         timer->flags |= TIMER_PINNED;
 
         new_base = get_timer_cpu_base(timer->flags, cpu);
 
         /*
          * If @timer was on a different CPU, it should be migrated with the
          * old base locked to prevent other operations proceeding with the
          * wrong base locked.  See lock_timer_base().
          */
         base = lock_timer_base(timer, &flags);
         /*
          * Has @timer been shutdown? This needs to be evaluated while
          * holding base lock to prevent a race against the shutdown code.
          */
         if (!timer->function)
                 goto out_unlock;
 
         if (base != new_base) {
                 timer->flags |= TIMER_MIGRATING;
 
                 raw_spin_unlock(&base->lock);
                 base = new_base;
                 raw_spin_lock(&base->lock);
                 WRITE_ONCE(timer->flags,
                            (timer->flags & ~TIMER_BASEMASK) | cpu);
         }
         forward_timer_base(base);
 
         debug_timer_activate(timer);
         internal_add_timer(base, timer);
 out_unlock:
         raw_spin_unlock_irqrestore(&base->lock, flags);
 }
 EXPORT_SYMBOL_GPL(add_timer_on);
 
 /**
  * __timer_delete - Internal function: Deactivate a timer
  * @timer:      The timer to be deactivated
  * @shutdown:   If true, this indicates that the timer is about to be
  *              shutdown permanently.
  *
  * If @shutdown is true then @timer->function is set to NULL under the
  * timer base lock which prevents further rearming of the time. In that
  * case any attempt to rearm @timer after this function returns will be
  * silently ignored.
  *
  * Return:
  * * %0 - The timer was not pending
  * * %1 - The timer was pending and deactivated
  */
 static int __timer_delete(struct timer_list *timer, bool shutdown)
 {
         struct timer_base *base;
         unsigned long flags;
         int ret = 0;
 
         debug_assert_init(timer);
 
         /*
          * If @shutdown is set then the lock has to be taken whether the
          * timer is pending or not to protect against a concurrent rearm
          * which might hit between the lockless pending check and the lock
          * acquisition. By taking the lock it is ensured that such a newly
          * enqueued timer is dequeued and cannot end up with
          * timer->function == NULL in the expiry code.
          *
          * If timer->function is currently executed, then this makes sure
          * that the callback cannot requeue the timer.
          */
         if (timer_pending(timer) || shutdown) {
                 base = lock_timer_base(timer, &flags);
                 ret = detach_if_pending(timer, base, true);
                 if (shutdown)
                         timer->function = NULL;
                 raw_spin_unlock_irqrestore(&base->lock, flags);
         }
 
         return ret;
 }
 
 /**
  * timer_delete - Deactivate a timer
  * @timer:      The timer to be deactivated
  *
  * The function only deactivates a pending timer, but contrary to
  * timer_delete_sync() it does not take into account whether the timer's
  * callback function is concurrently executed on a different CPU or not.
  * It neither prevents rearming of the timer.  If @timer can be rearmed
  * concurrently then the return value of this function is meaningless.
  *
  * Return:
  * * %0 - The timer was not pending
  * * %1 - The timer was pending and deactivated
  */
 int timer_delete(struct timer_list *timer)
 {
         return __timer_delete(timer, false);
 }
 EXPORT_SYMBOL(timer_delete);
 
 /**
  * timer_shutdown - Deactivate a timer and prevent rearming
  * @timer:      The timer to be deactivated
  *
  * The function does not wait for an eventually running timer callback on a
  * different CPU but it prevents rearming of the timer. Any attempt to arm
  * @timer after this function returns will be silently ignored.
  *
  * This function is useful for teardown code and should only be used when
  * timer_shutdown_sync() cannot be invoked due to locking or context constraints.
  *
  * Return:
  * * %0 - The timer was not pending
  * * %1 - The timer was pending
  */
 int timer_shutdown(struct timer_list *timer)
 {
         return __timer_delete(timer, true);
 }
 EXPORT_SYMBOL_GPL(timer_shutdown);
 
 /**
  * __try_to_del_timer_sync - Internal function: Try to deactivate a timer
  * @timer:      Timer to deactivate
  * @shutdown:   If true, this indicates that the timer is about to be
  *              shutdown permanently.
  *
  * If @shutdown is true then @timer->function is set to NULL under the
  * timer base lock which prevents further rearming of the timer. Any
  * attempt to rearm @timer after this function returns will be silently
  * ignored.
  *
  * This function cannot guarantee that the timer cannot be rearmed
  * right after dropping the base lock if @shutdown is false. That
  * needs to be prevented by the calling code if necessary.
  *
  * Return:
  * * %0  - The timer was not pending
  * * %1  - The timer was pending and deactivated
  * * %-1 - The timer callback function is running on a different CPU
  */
 static int __try_to_del_timer_sync(struct timer_list *timer, bool shutdown)
 {
         struct timer_base *base;
         unsigned long flags;
         int ret = -1;
 
         debug_assert_init(timer);
 
         base = lock_timer_base(timer, &flags);
 
         if (base->running_timer != timer)
                 ret = detach_if_pending(timer, base, true);
         if (shutdown)
                 timer->function = NULL;
 
         raw_spin_unlock_irqrestore(&base->lock, flags);
 
         return ret;
 }
 
 /**
  * try_to_del_timer_sync - Try to deactivate a timer
  * @timer:      Timer to deactivate
  *
  * This function tries to deactivate a timer. On success the timer is not
  * queued and the timer callback function is not running on any CPU.
  *
  * This function does not guarantee that the timer cannot be rearmed right
  * after dropping the base lock. That needs to be prevented by the calling
  * code if necessary.
  *
  * Return:
  * * %0  - The timer was not pending
  * * %1  - The timer was pending and deactivated
  * * %-1 - The timer callback function is running on a different CPU
  */
 int try_to_del_timer_sync(struct timer_list *timer)
 {
         return __try_to_del_timer_sync(timer, false);
 }
 EXPORT_SYMBOL(try_to_del_timer_sync);
 
 #ifdef CONFIG_PREEMPT_RT
 static __init void timer_base_init_expiry_lock(struct timer_base *base)
 {
         spin_lock_init(&base->expiry_lock);
 }
 
 static inline void timer_base_lock_expiry(struct timer_base *base)
 {
         spin_lock(&base->expiry_lock);
 }
 
 static inline void timer_base_unlock_expiry(struct timer_base *base)
 {
         spin_unlock(&base->expiry_lock);
 }
 
 /*
  * The counterpart to del_timer_wait_running().
  *
  * If there is a waiter for base->expiry_lock, then it was waiting for the
  * timer callback to finish. Drop expiry_lock and reacquire it. That allows
  * the waiter to acquire the lock and make progress.
  */
 static void timer_sync_wait_running(struct timer_base *base)
 {
         if (atomic_read(&base->timer_waiters)) {
                 raw_spin_unlock_irq(&base->lock);
                 spin_unlock(&base->expiry_lock);
                 spin_lock(&base->expiry_lock);
                 raw_spin_lock_irq(&base->lock);
         }
 }
 
 /*
  * This function is called on PREEMPT_RT kernels when the fast path
  * deletion of a timer failed because the timer callback function was
  * running.
  *
  * This prevents priority inversion, if the softirq thread on a remote CPU
  * got preempted, and it prevents a life lock when the task which tries to
  * delete a timer preempted the softirq thread running the timer callback
  * function.
  */
 static void del_timer_wait_running(struct timer_list *timer)
 {
         u32 tf;
 
         tf = READ_ONCE(timer->flags);
         if (!(tf & (TIMER_MIGRATING | TIMER_IRQSAFE))) {
                 struct timer_base *base = get_timer_base(tf);
 
                 /*
                  * Mark the base as contended and grab the expiry lock,
                  * which is held by the softirq across the timer
                  * callback. Drop the lock immediately so the softirq can
                  * expire the next timer. In theory the timer could already
                  * be running again, but that's more than unlikely and just
                  * causes another wait loop.
                  */
                 atomic_inc(&base->timer_waiters);
                 spin_lock_bh(&base->expiry_lock);
                 atomic_dec(&base->timer_waiters);
                 spin_unlock_bh(&base->expiry_lock);
         }
 }
 #else
 static inline void timer_base_init_expiry_lock(struct timer_base *base) { }
 static inline void timer_base_lock_expiry(struct timer_base *base) { }
 static inline void timer_base_unlock_expiry(struct timer_base *base) { }
 static inline void timer_sync_wait_running(struct timer_base *base) { }
 static inline void del_timer_wait_running(struct timer_list *timer) { }
 #endif
 
 /**
  * __timer_delete_sync - Internal function: Deactivate a timer and wait
  *                       for the handler to finish.
  * @timer:      The timer to be deactivated
  * @shutdown:   If true, @timer->function will be set to NULL under the
  *              timer base lock which prevents rearming of @timer
  *
  * If @shutdown is not set the timer can be rearmed later. If the timer can
  * be rearmed concurrently, i.e. after dropping the base lock then the
  * return value is meaningless.
  *
  * If @shutdown is set then @timer->function is set to NULL under timer
  * base lock which prevents rearming of the timer. Any attempt to rearm
  * a shutdown timer is silently ignored.
  *
  * If the timer should be reused after shutdown it has to be initialized
  * again.
  *
  * Return:
  * * %0 - The timer was not pending
  * * %1 - The timer was pending and deactivated
  */
 static int __timer_delete_sync(struct timer_list *timer, bool shutdown)
 {
         int ret;
 
 #ifdef CONFIG_LOCKDEP
         unsigned long flags;
 
         /*
          * If lockdep gives a backtrace here, please reference
          * the synchronization rules above.
          */
         local_irq_save(flags);
         lock_map_acquire(&timer->lockdep_map);
         lock_map_release(&timer->lockdep_map);
         local_irq_restore(flags);
 #endif
         /*
          * don't use it in hardirq context, because it
          * could lead to deadlock.
          */
         WARN_ON(in_hardirq() && !(timer->flags & TIMER_IRQSAFE));
 
         /*
          * Must be able to sleep on PREEMPT_RT because of the slowpath in
          * del_timer_wait_running().
          */
         if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(timer->flags & TIMER_IRQSAFE))
                 lockdep_assert_preemption_enabled();
 
         do {
                 ret = __try_to_del_timer_sync(timer, shutdown);
 
                 if (unlikely(ret < 0)) {
                         del_timer_wait_running(timer);
                         cpu_relax();
                 }
         } while (ret < 0);
 
         return ret;
 }
 
 /**
  * timer_delete_sync - Deactivate a timer and wait for the handler to finish.
  * @timer:      The timer to be deactivated
  *
  * Synchronization rules: Callers must prevent restarting of the timer,
  * otherwise this function is meaningless. It must not be called from
  * interrupt contexts unless the timer is an irqsafe one. The caller must
  * not hold locks which would prevent completion of the timer's callback
  * function. The timer's handler must not call add_timer_on(). Upon exit
  * the timer is not queued and the handler is not running on any CPU.
  *
  * For !irqsafe timers, the caller must not hold locks that are held in
  * interrupt context. Even if the lock has nothing to do with the timer in
  * question.  Here's why::
  *
  *    CPU0                             CPU1
  *    ----                             ----
  *                                     <SOFTIRQ>
  *                                       call_timer_fn();
  *                                       base->running_timer = mytimer;
  *    spin_lock_irq(somelock);
  *                                     <IRQ>
  *                                        spin_lock(somelock);
  *    timer_delete_sync(mytimer);
  *    while (base->running_timer == mytimer);
  *
  * Now timer_delete_sync() will never return and never release somelock.
  * The interrupt on the other CPU is waiting to grab somelock but it has
  * interrupted the softirq that CPU0 is waiting to finish.
  *
  * This function cannot guarantee that the timer is not rearmed again by
  * some concurrent or preempting code, right after it dropped the base
  * lock. If there is the possibility of a concurrent rearm then the return
  * value of the function is meaningless.
  *
  * If such a guarantee is needed, e.g. for teardown situations then use
  * timer_shutdown_sync() instead.
  *
  * Return:
  * * %0 - The timer was not pending
  * * %1 - The timer was pending and deactivated
  */
 int timer_delete_sync(struct timer_list *timer)
 {
         return __timer_delete_sync(timer, false);
 }
 EXPORT_SYMBOL(timer_delete_sync);
 
 /**
  * timer_shutdown_sync - Shutdown a timer and prevent rearming
  * @timer: The timer to be shutdown
  *
  * When the function returns it is guaranteed that:
  *   - @timer is not queued
  *   - The callback function of @timer is not running
  *   - @timer cannot be enqueued again. Any attempt to rearm
  *     @timer is silently ignored.
  *
  * See timer_delete_sync() for synchronization rules.
  *
  * This function is useful for final teardown of an infrastructure where
  * the timer is subject to a circular dependency problem.
  *
  * A common pattern for this is a timer and a workqueue where the timer can
  * schedule work and work can arm the timer. On shutdown the workqueue must
  * be destroyed and the timer must be prevented from rearming. Unless the
  * code has conditionals like 'if (mything->in_shutdown)' to prevent that
  * there is no way to get this correct with timer_delete_sync().
  *
  * timer_shutdown_sync() is solving the problem. The correct ordering of
  * calls in this case is:
  *
  *      timer_shutdown_sync(&mything->timer);
  *      workqueue_destroy(&mything->workqueue);
  *
  * After this 'mything' can be safely freed.
  *
  * This obviously implies that the timer is not required to be functional
  * for the rest of the shutdown operation.
  *
  * Return:
  * * %0 - The timer was not pending
  * * %1 - The timer was pending
  */
 int timer_shutdown_sync(struct timer_list *timer)
 {
         return __timer_delete_sync(timer, true);
 }
 EXPORT_SYMBOL_GPL(timer_shutdown_sync);
 
 static void call_timer_fn(struct timer_list *timer,
                           void (*fn)(struct timer_list *),
                           unsigned long baseclk)
 {
         int count = preempt_count();
 
 #ifdef CONFIG_LOCKDEP
         /*
          * It is permissible to free the timer from inside the
          * function that is called from it, this we need to take into
          * account for lockdep too. To avoid bogus "held lock freed"
          * warnings as well as problems when looking into
          * timer->lockdep_map, make a copy and use that here.
          */
         struct lockdep_map lockdep_map;
 
         lockdep_copy_map(&lockdep_map, &timer->lockdep_map);
 #endif
         /*
          * Couple the lock chain with the lock chain at
          * timer_delete_sync() by acquiring the lock_map around the fn()
          * call here and in timer_delete_sync().
          */
         lock_map_acquire(&lockdep_map);
 
         trace_timer_expire_entry(timer, baseclk);
         fn(timer);
         trace_timer_expire_exit(timer);
 
         lock_map_release(&lockdep_map);
 
         if (count != preempt_count()) {
                 WARN_ONCE(1, "timer: %pS preempt leak: %08x -> %08x\n",
                           fn, count, preempt_count());
                 /*
                  * Restore the preempt count. That gives us a decent
                  * chance to survive and extract information. If the
                  * callback kept a lock held, bad luck, but not worse
                  * than the BUG() we had.
                  */
                 preempt_count_set(count);
         }
 }
 
 static void expire_timers(struct timer_base *base, struct hlist_head *head)
 {
         /*
          * This value is required only for tracing. base->clk was
          * incremented directly before expire_timers was called. But expiry
          * is related to the old base->clk value.
          */
         unsigned long baseclk = base->clk - 1;
 
         while (!hlist_empty(head)) {
                 struct timer_list *timer;
                 void (*fn)(struct timer_list *);
 
                 timer = hlist_entry(head->first, struct timer_list, entry);
 
                 base->running_timer = timer;
                 detach_timer(timer, true);
 
                 fn = timer->function;
 
                 if (WARN_ON_ONCE(!fn)) {
                         /* Should never happen. Emphasis on should! */
                         base->running_timer = NULL;
                         continue;
                 }
 
                 if (timer->flags & TIMER_IRQSAFE) {
                         raw_spin_unlock(&base->lock);
                         call_timer_fn(timer, fn, baseclk);
                         raw_spin_lock(&base->lock);
                         base->running_timer = NULL;
                 } else {
                         raw_spin_unlock_irq(&base->lock);
                         call_timer_fn(timer, fn, baseclk);
                         raw_spin_lock_irq(&base->lock);
                         base->running_timer = NULL;
                         timer_sync_wait_running(base);
                 }
         }
 }
 
 static int collect_expired_timers(struct timer_base *base,
                                   struct hlist_head *heads)
 {
         unsigned long clk = base->clk = base->next_expiry;
         struct hlist_head *vec;
         int i, levels = 0;
         unsigned int idx;
 
         for (i = 0; i < LVL_DEPTH; i++) {
                 idx = (clk & LVL_MASK) + i * LVL_SIZE;
 
                 if (__test_and_clear_bit(idx, base->pending_map)) {
                         vec = base->vectors + idx;
                         hlist_move_list(vec, heads++);
                         levels++;
                 }
                 /* Is it time to look at the next level? */
                 if (clk & LVL_CLK_MASK)
                         break;
                 /* Shift clock for the next level granularity */
                 clk >>= LVL_CLK_SHIFT;
         }
         return levels;
 }
 
 /*
  * Find the next pending bucket of a level. Search from level start (@offset)
  * + @clk upwards and if nothing there, search from start of the level
  * (@offset) up to @offset + clk.
  */
 static int next_pending_bucket(struct timer_base *base, unsigned offset,
                                unsigned clk)
 {
         unsigned pos, start = offset + clk;
         unsigned end = offset + LVL_SIZE;
 
         pos = find_next_bit(base->pending_map, end, start);
         if (pos < end)
                 return pos - start;
 
         pos = find_next_bit(base->pending_map, start, offset);
         return pos < start ? pos + LVL_SIZE - start : -1;
 }
 
 /*
  * Search the first expiring timer in the various clock levels. Caller must
  * hold base->lock.
  *
  * Store next expiry time in base->next_expiry.
  */
 static void next_expiry_recalc(struct timer_base *base)
 {
         unsigned long clk, next, adj;
         unsigned lvl, offset = 0;
 
         next = base->clk + NEXT_TIMER_MAX_DELTA;
         clk = base->clk;
         for (lvl = 0; lvl < LVL_DEPTH; lvl++, offset += LVL_SIZE) {
                 int pos = next_pending_bucket(base, offset, clk & LVL_MASK);
                 unsigned long lvl_clk = clk & LVL_CLK_MASK;
 
                 if (pos >= 0) {
                         unsigned long tmp = clk + (unsigned long) pos;
 
                         tmp <<= LVL_SHIFT(lvl);
                         if (time_before(tmp, next))
                                 next = tmp;
 
                         /*
                          * If the next expiration happens before we reach
                          * the next level, no need to check further.
                          */
                         if (pos <= ((LVL_CLK_DIV - lvl_clk) & LVL_CLK_MASK))
                                 break;
                 }
                 /*
                  * Clock for the next level. If the current level clock lower
                  * bits are zero, we look at the next level as is. If not we
                  * need to advance it by one because that's going to be the
                  * next expiring bucket in that level. base->clk is the next
                  * expiring jiffie. So in case of:
                  *
                  * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
                  *  0    0    0    0    0    0
                  *
                  * we have to look at all levels @index 0. With
                  *
                  * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
                  *  0    0    0    0    0    2
                  *
                  * LVL0 has the next expiring bucket @index 2. The upper
                  * levels have the next expiring bucket @index 1.
                  *
                  * In case that the propagation wraps the next level the same
                  * rules apply:
                  *
                  * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
                  *  0    0    0    0    F    2
                  *
                  * So after looking at LVL0 we get:
                  *
                  * LVL5 LVL4 LVL3 LVL2 LVL1
                  *  0    0    0    1    0
                  *
                  * So no propagation from LVL1 to LVL2 because that happened
                  * with the add already, but then we need to propagate further
                  * from LVL2 to LVL3.
                  *
                  * So the simple check whether the lower bits of the current
                  * level are 0 or not is sufficient for all cases.
                  */
                 adj = lvl_clk ? 1 : 0;
                 clk >>= LVL_CLK_SHIFT;
                 clk += adj;
         }
 
         base->next_expiry = next;
         base->next_expiry_recalc = false;
         base->timers_pending = !(next == base->clk + NEXT_TIMER_MAX_DELTA);
 }
 
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * Check, if the next hrtimer event is before the next timer wheel
  * event:
  */
 static u64 cmp_next_hrtimer_event(u64 basem, u64 expires)
 {
         u64 nextevt = hrtimer_get_next_event();
 
         /*
          * If high resolution timers are enabled
          * hrtimer_get_next_event() returns KTIME_MAX.
          */
         if (expires <= nextevt)
                 return expires;
 
         /*
          * If the next timer is already expired, return the tick base
          * time so the tick is fired immediately.
          */
         if (nextevt <= basem)
                 return basem;
 
         /*
          * Round up to the next jiffie. High resolution timers are
          * off, so the hrtimers are expired in the tick and we need to
          * make sure that this tick really expires the timer to avoid
          * a ping pong of the nohz stop code.
          *
          * Use DIV_ROUND_UP_ULL to prevent gcc calling __divdi3
          */
         return DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC;
 }
 
 static unsigned long next_timer_interrupt(struct timer_base *base,
                                           unsigned long basej)
 {
         if (base->next_expiry_recalc)
                 next_expiry_recalc(base);
 
         /*
          * Move next_expiry for the empty base into the future to prevent an
          * unnecessary raise of the timer softirq when the next_expiry value
          * will be reached even if there is no timer pending.
          *
          * This update is also required to make timer_base::next_expiry values
          * easy comparable to find out which base holds the first pending timer.
          */
         if (!base->timers_pending)
                 base->next_expiry = basej + NEXT_TIMER_MAX_DELTA;
 
         return base->next_expiry;
 }
 
 static unsigned long fetch_next_timer_interrupt(unsigned long basej, u64 basem,
                                                 struct timer_base *base_local,
                                                 struct timer_base *base_global,
                                                 struct timer_events *tevt)
 {
         unsigned long nextevt, nextevt_local, nextevt_global;
         bool local_first;
 
         nextevt_local = next_timer_interrupt(base_local, basej);
         nextevt_global = next_timer_interrupt(base_global, basej);
 
         local_first = time_before_eq(nextevt_local, nextevt_global);
 
         nextevt = local_first ? nextevt_local : nextevt_global;
 
         /*
          * If the @nextevt is at max. one tick away, use @nextevt and store
          * it in the local expiry value. The next global event is irrelevant in
          * this case and can be left as KTIME_MAX.
          */
         if (time_before_eq(nextevt, basej + 1)) {
                 /* If we missed a tick already, force 0 delta */
                 if (time_before(nextevt, basej))
                         nextevt = basej;
                 tevt->local = basem + (u64)(nextevt - basej) * TICK_NSEC;
 
                 /*
                  * This is required for the remote check only but it doesn't
                  * hurt, when it is done for both call sites:
                  *
                  * * The remote callers will only take care of the global timers
                  *   as local timers will be handled by CPU itself. When not
                  *   updating tevt->global with the already missed first global
                  *   timer, it is possible that it will be missed completely.
                  *
                  * * The local callers will ignore the tevt->global anyway, when
                  *   nextevt is max. one tick away.
                  */
                 if (!local_first)
                         tevt->global = tevt->local;
                 return nextevt;
         }
 
         /*
          * Update tevt.* values:
          *
          * If the local queue expires first, then the global event can be
          * ignored. If the global queue is empty, nothing to do either.
          */
         if (!local_first && base_global->timers_pending)
                 tevt->global = basem + (u64)(nextevt_global - basej) * TICK_NSEC;
 
         if (base_local->timers_pending)
                 tevt->local = basem + (u64)(nextevt_local - basej) * TICK_NSEC;
 
         return nextevt;
 }
 
 # ifdef CONFIG_SMP
 /**
  * fetch_next_timer_interrupt_remote() - Store next timers into @tevt
  * @basej:      base time jiffies
  * @basem:      base time clock monotonic
  * @tevt:       Pointer to the storage for the expiry values
  * @cpu:        Remote CPU
  *
  * Stores the next pending local and global timer expiry values in the
  * struct pointed to by @tevt. If a queue is empty the corresponding
  * field is set to KTIME_MAX. If local event expires before global
  * event, global event is set to KTIME_MAX as well.
  *
  * Caller needs to make sure timer base locks are held (use
  * timer_lock_remote_bases() for this purpose).
  */
 void fetch_next_timer_interrupt_remote(unsigned long basej, u64 basem,
                                        struct timer_events *tevt,
                                        unsigned int cpu)
 {
         struct timer_base *base_local, *base_global;
 
         /* Preset local / global events */
         tevt->local = tevt->global = KTIME_MAX;
 
         base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
         base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
 
         lockdep_assert_held(&base_local->lock);
         lockdep_assert_held(&base_global->lock);
 
         fetch_next_timer_interrupt(basej, basem, base_local, base_global, tevt);
 }
 
 /**
  * timer_unlock_remote_bases - unlock timer bases of cpu
  * @cpu:        Remote CPU
  *
  * Unlocks the remote timer bases.
  */
 void timer_unlock_remote_bases(unsigned int cpu)
         __releases(timer_bases[BASE_LOCAL]->lock)
         __releases(timer_bases[BASE_GLOBAL]->lock)
 {
         struct timer_base *base_local, *base_global;
 
         base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
         base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
 
         raw_spin_unlock(&base_global->lock);
         raw_spin_unlock(&base_local->lock);
 }
 
 /**
  * timer_lock_remote_bases - lock timer bases of cpu
  * @cpu:        Remote CPU
  *
  * Locks the remote timer bases.
  */
 void timer_lock_remote_bases(unsigned int cpu)
         __acquires(timer_bases[BASE_LOCAL]->lock)
         __acquires(timer_bases[BASE_GLOBAL]->lock)
 {
         struct timer_base *base_local, *base_global;
 
         base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
         base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
 
         lockdep_assert_irqs_disabled();
 
         raw_spin_lock(&base_local->lock);
         raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
 }
 
 /**
  * timer_base_is_idle() - Return whether timer base is set idle
  *
  * Returns value of local timer base is_idle value.
  */
 bool timer_base_is_idle(void)
 {
         return __this_cpu_read(timer_bases[BASE_LOCAL].is_idle);
 }
 
 static void __run_timer_base(struct timer_base *base);
 
 /**
  * timer_expire_remote() - expire global timers of cpu
  * @cpu:        Remote CPU
  *
  * Expire timers of global base of remote CPU.
  */
 void timer_expire_remote(unsigned int cpu)
 {
         struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
 
         __run_timer_base(base);
 }
 
 static void timer_use_tmigr(unsigned long basej, u64 basem,
                             unsigned long *nextevt, bool *tick_stop_path,
                             bool timer_base_idle, struct timer_events *tevt)
 {
         u64 next_tmigr;
 
         if (timer_base_idle)
                 next_tmigr = tmigr_cpu_new_timer(tevt->global);
         else if (tick_stop_path)
                 next_tmigr = tmigr_cpu_deactivate(tevt->global);
         else
                 next_tmigr = tmigr_quick_check(tevt->global);
 
         /*
          * If the CPU is the last going idle in timer migration hierarchy, make
          * sure the CPU will wake up in time to handle remote timers.
          * next_tmigr == KTIME_MAX if other CPUs are still active.
          */
         if (next_tmigr < tevt->local) {
                 u64 tmp;
 
                 /* If we missed a tick already, force 0 delta */
                 if (next_tmigr < basem)
                         next_tmigr = basem;
 
                 tmp = div_u64(next_tmigr - basem, TICK_NSEC);
 
                 *nextevt = basej + (unsigned long)tmp;
                 tevt->local = next_tmigr;
         }
 }
 # else
 static void timer_use_tmigr(unsigned long basej, u64 basem,
                             unsigned long *nextevt, bool *tick_stop_path,
                             bool timer_base_idle, struct timer_events *tevt)
 {
         /*
          * Make sure first event is written into tevt->local to not miss a
          * timer on !SMP systems.
          */
         tevt->local = min_t(u64, tevt->local, tevt->global);
 }
 # endif /* CONFIG_SMP */
 
 static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
                                              bool *idle)
 {
         struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX };
         struct timer_base *base_local, *base_global;
         unsigned long nextevt;
         bool idle_is_possible;
 
         /*
          * When the CPU is offline, the tick is cancelled and nothing is supposed
          * to try to stop it.
          */
         if (WARN_ON_ONCE(cpu_is_offline(smp_processor_id()))) {
                 if (idle)
                         *idle = true;
                 return tevt.local;
         }
 
         base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
         base_global = this_cpu_ptr(&timer_bases[BASE_GLOBAL]);
 
         raw_spin_lock(&base_local->lock);
         raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
 
         nextevt = fetch_next_timer_interrupt(basej, basem, base_local,
                                              base_global, &tevt);
 
         /*
          * If the next event is only one jiffie ahead there is no need to call
          * timer migration hierarchy related functions. The value for the next
          * global timer in @tevt struct equals then KTIME_MAX. This is also
          * true, when the timer base is idle.
          *
          * The proper timer migration hierarchy function depends on the callsite
          * and whether timer base is idle or not. @nextevt will be updated when
          * this CPU needs to handle the first timer migration hierarchy
          * event. See timer_use_tmigr() for detailed information.
          */
         idle_is_possible = time_after(nextevt, basej + 1);
         if (idle_is_possible)
                 timer_use_tmigr(basej, basem, &nextevt, idle,
                                 base_local->is_idle, &tevt);
 
         /*
          * We have a fresh next event. Check whether we can forward the
          * base.
          */
         __forward_timer_base(base_local, basej);
         __forward_timer_base(base_global, basej);
 
         /*
          * Set base->is_idle only when caller is timer_base_try_to_set_idle()
          */
         if (idle) {
                 /*
                  * Bases are idle if the next event is more than a tick
                  * away. Caution: @nextevt could have changed by enqueueing a
                  * global timer into timer migration hierarchy. Therefore a new
                  * check is required here.
                  *
                  * If the base is marked idle then any timer add operation must
                  * forward the base clk itself to keep granularity small. This
                  * idle logic is only maintained for the BASE_LOCAL and
                  * BASE_GLOBAL base, deferrable timers may still see large
                  * granularity skew (by design).
                  */
                 if (!base_local->is_idle && time_after(nextevt, basej + 1)) {
                         base_local->is_idle = true;
                         /*
                          * Global timers queued locally while running in a task
                          * in nohz_full mode need a self-IPI to kick reprogramming
                          * in IRQ tail.
                          */
                         if (tick_nohz_full_cpu(base_local->cpu))
                                 base_global->is_idle = true;
                         trace_timer_base_idle(true, base_local->cpu);
                 }
                 *idle = base_local->is_idle;
 
                 /*
                  * When timer base is not set idle, undo the effect of
                  * tmigr_cpu_deactivate() to prevent inconsistent states - active
                  * timer base but inactive timer migration hierarchy.
                  *
                  * When timer base was already marked idle, nothing will be
                  * changed here.
                  */
                 if (!base_local->is_idle && idle_is_possible)
                         tmigr_cpu_activate();
         }
 
         raw_spin_unlock(&base_global->lock);
         raw_spin_unlock(&base_local->lock);
 
         return cmp_next_hrtimer_event(basem, tevt.local);
 }
 
 /**
  * get_next_timer_interrupt() - return the time (clock mono) of the next timer
  * @basej:      base time jiffies
  * @basem:      base time clock monotonic
  *
  * Returns the tick aligned clock monotonic time of the next pending timer or
  * KTIME_MAX if no timer is pending. If timer of global base was queued into
  * timer migration hierarchy, first global timer is not taken into account. If
  * it was the last CPU of timer migration hierarchy going idle, first global
  * event is taken into account.
  */
 u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 {
         return __get_next_timer_interrupt(basej, basem, NULL);
 }
 
 /**
  * timer_base_try_to_set_idle() - Try to set the idle state of the timer bases
  * @basej:      base time jiffies
  * @basem:      base time clock monotonic
  * @idle:       pointer to store the value of timer_base->is_idle on return;
  *              *idle contains the information whether tick was already stopped
  *
  * Returns the tick aligned clock monotonic time of the next pending timer or
  * KTIME_MAX if no timer is pending. When tick was already stopped KTIME_MAX is
  * returned as well.
  */
 u64 timer_base_try_to_set_idle(unsigned long basej, u64 basem, bool *idle)
 {
         if (*idle)
                 return KTIME_MAX;
 
         return __get_next_timer_interrupt(basej, basem, idle);
 }
 
 /**
  * timer_clear_idle - Clear the idle state of the timer base
  *
  * Called with interrupts disabled
  */
 void timer_clear_idle(void)
 {
         /*
          * We do this unlocked. The worst outcome is a remote pinned timer
          * enqueue sending a pointless IPI, but taking the lock would just
          * make the window for sending the IPI a few instructions smaller
          * for the cost of taking the lock in the exit from idle
          * path. Required for BASE_LOCAL only.
          */
         __this_cpu_write(timer_bases[BASE_LOCAL].is_idle, false);
         if (tick_nohz_full_cpu(smp_processor_id()))
                 __this_cpu_write(timer_bases[BASE_GLOBAL].is_idle, false);
         trace_timer_base_idle(false, smp_processor_id());
 
         /* Activate without holding the timer_base->lock */
         tmigr_cpu_activate();
 }
 #endif
 
 /**
  * __run_timers - run all expired timers (if any) on this CPU.
  * @base: the timer vector to be processed.
  */
 static inline void __run_timers(struct timer_base *base)
 {
         struct hlist_head heads[LVL_DEPTH];
         int levels;
 
         lockdep_assert_held(&base->lock);
 
         if (base->running_timer)
                 return;
 
         while (time_after_eq(jiffies, base->clk) &&
                time_after_eq(jiffies, base->next_expiry)) {
                 levels = collect_expired_timers(base, heads);
                 /*
                  * The two possible reasons for not finding any expired
                  * timer at this clk are that all matching timers have been
                  * dequeued or no timer has been queued since
                  * base::next_expiry was set to base::clk +
                  * NEXT_TIMER_MAX_DELTA.
                  */
                 WARN_ON_ONCE(!levels && !base->next_expiry_recalc
                              && base->timers_pending);
                 /*
                  * While executing timers, base->clk is set 1 offset ahead of
                  * jiffies to avoid endless requeuing to current jiffies.
                  */
                 base->clk++;
                 next_expiry_recalc(base);
 
                 while (levels--)
                         expire_timers(base, heads + levels);
         }
 }
 
 static void __run_timer_base(struct timer_base *base)
 {
         if (time_before(jiffies, base->next_expiry))
                 return;
 
         timer_base_lock_expiry(base);
         raw_spin_lock_irq(&base->lock);
         __run_timers(base);
         raw_spin_unlock_irq(&base->lock);
         timer_base_unlock_expiry(base);
 }
 
 static void run_timer_base(int index)
 {
         struct timer_base *base = this_cpu_ptr(&timer_bases[index]);
 
         __run_timer_base(base);
 }
 
 /*
  * This function runs timers and the timer-tq in bottom half context.
  */
 static __latent_entropy void run_timer_softirq(struct softirq_action *h)
 {
         run_timer_base(BASE_LOCAL);
         if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) {
                 run_timer_base(BASE_GLOBAL);
                 run_timer_base(BASE_DEF);
 
                 if (is_timers_nohz_active())
                         tmigr_handle_remote();
         }
 }
 
 /*
  * Called by the local, per-CPU timer interrupt on SMP.
  */
 static void run_local_timers(void)
 {
         struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
 
         hrtimer_run_queues();
 
         for (int i = 0; i < NR_BASES; i++, base++) {
                 /* Raise the softirq only if required. */
                 if (time_after_eq(jiffies, base->next_expiry) ||
                     (i == BASE_DEF && tmigr_requires_handle_remote())) {
                         raise_softirq(TIMER_SOFTIRQ);
                         return;
                 }
         }
 }
 
 /*
  * Called from the timer interrupt handler to charge one tick to the current
  * process.  user_tick is 1 if the tick is user time, 0 for system.
  */
 void update_process_times(int user_tick)
 {
         struct task_struct *p = current;
 
         /* Note: this timer irq context must be accounted for as well. */
         account_process_tick(p, user_tick);
         run_local_timers();
         rcu_sched_clock_irq(user_tick);
 #ifdef CONFIG_IRQ_WORK
         if (in_irq())
                 irq_work_tick();
 #endif
         sched_tick();
         if (IS_ENABLED(CONFIG_POSIX_TIMERS))
                 run_posix_cpu_timers();
 }
 
 /*
  * Since schedule_timeout()'s timer is defined on the stack, it must store
  * the target task on the stack as well.
  */
 struct process_timer {
         struct timer_list timer;
         struct task_struct *task;
 };
 
 static void process_timeout(struct timer_list *t)
 {
         struct process_timer *timeout = from_timer(timeout, t, timer);
 
         wake_up_process(timeout->task);
 }
 
 /**
  * schedule_timeout - sleep until timeout
  * @timeout: timeout value in jiffies
  *
  * Make the current task sleep until @timeout jiffies have elapsed.
  * The function behavior depends on the current task state
  * (see also set_current_state() description):
  *
  * %TASK_RUNNING - the scheduler is called, but the task does not sleep
  * at all. That happens because sched_submit_work() does nothing for
  * tasks in %TASK_RUNNING state.
  *
  * %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to
  * pass before the routine returns unless the current task is explicitly
  * woken up, (e.g. by wake_up_process()).
  *
  * %TASK_INTERRUPTIBLE - the routine may return early if a signal is
  * delivered to the current task or the current task is explicitly woken
  * up.
  *
  * The current task state is guaranteed to be %TASK_RUNNING when this
  * routine returns.
  *
  * Specifying a @timeout value of %MAX_SCHEDULE_TIMEOUT will schedule
  * the CPU away without a bound on the timeout. In this case the return
  * value will be %MAX_SCHEDULE_TIMEOUT.
  *
  * Returns 0 when the timer has expired otherwise the remaining time in
  * jiffies will be returned. In all cases the return value is guaranteed
  * to be non-negative.
  */
 signed long __sched schedule_timeout(signed long timeout)
 {
         struct process_timer timer;
         unsigned long expire;
 
         switch (timeout)
         {
         case MAX_SCHEDULE_TIMEOUT:
                 /*
                  * These two special cases are useful to be comfortable
                  * in the caller. Nothing more. We could take
                  * MAX_SCHEDULE_TIMEOUT from one of the negative value
                  * but I' d like to return a valid offset (>=0) to allow
                  * the caller to do everything it want with the retval.
                  */
                 schedule();
                 goto out;
         default:
                 /*
                  * Another bit of PARANOID. Note that the retval will be
                  * 0 since no piece of kernel is supposed to do a check
                  * for a negative retval of schedule_timeout() (since it
                  * should never happens anyway). You just have the printk()
                  * that will tell you if something is gone wrong and where.
                  */
                 if (timeout < 0) {
                         printk(KERN_ERR "schedule_timeout: wrong timeout "
                                 "value %lx\n", timeout);
                         dump_stack();
                         __set_current_state(TASK_RUNNING);
                         goto out;
                 }
         }
 
         expire = timeout + jiffies;
 
         timer.task = current;
         timer_setup_on_stack(&timer.timer, process_timeout, 0);
         __mod_timer(&timer.timer, expire, MOD_TIMER_NOTPENDING);
         schedule();
         del_timer_sync(&timer.timer);
 
         /* Remove the timer from the object tracker */
         destroy_timer_on_stack(&timer.timer);
 
         timeout = expire - jiffies;
 
  out:
         return timeout < 0 ? 0 : timeout;
 }
 EXPORT_SYMBOL(schedule_timeout);
 
 /*
  * We can use __set_current_state() here because schedule_timeout() calls
  * schedule() unconditionally.
  */
 signed long __sched schedule_timeout_interruptible(signed long timeout)
 {
         __set_current_state(TASK_INTERRUPTIBLE);
         return schedule_timeout(timeout);
 }
 EXPORT_SYMBOL(schedule_timeout_interruptible);
 
 signed long __sched schedule_timeout_killable(signed long timeout)
 {
         __set_current_state(TASK_KILLABLE);
         return schedule_timeout(timeout);
 }
 EXPORT_SYMBOL(schedule_timeout_killable);
 
 signed long __sched schedule_timeout_uninterruptible(signed long timeout)
 {
         __set_current_state(TASK_UNINTERRUPTIBLE);
         return schedule_timeout(timeout);
 }
 EXPORT_SYMBOL(schedule_timeout_uninterruptible);
 
 /*
  * Like schedule_timeout_uninterruptible(), except this task will not contribute
  * to load average.
  */
 signed long __sched schedule_timeout_idle(signed long timeout)
 {
         __set_current_state(TASK_IDLE);
         return schedule_timeout(timeout);
 }
 EXPORT_SYMBOL(schedule_timeout_idle);
 
 #ifdef CONFIG_HOTPLUG_CPU
 static void migrate_timer_list(struct timer_base *new_base, struct hlist_head *head)
 {
         struct timer_list *timer;
         int cpu = new_base->cpu;
 
         while (!hlist_empty(head)) {
                 timer = hlist_entry(head->first, struct timer_list, entry);
                 detach_timer(timer, false);
                 timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
                 internal_add_timer(new_base, timer);
         }
 }
 
 int timers_prepare_cpu(unsigned int cpu)
 {
         struct timer_base *base;
         int b;
 
         for (b = 0; b < NR_BASES; b++) {
                 base = per_cpu_ptr(&timer_bases[b], cpu);
                 base->clk = jiffies;
                 base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
                 base->next_expiry_recalc = false;
                 base->timers_pending = false;
                 base->is_idle = false;
         }
         return 0;
 }
 
 int timers_dead_cpu(unsigned int cpu)
 {
         struct timer_base *old_base;
         struct timer_base *new_base;
         int b, i;
 
         for (b = 0; b < NR_BASES; b++) {
                 old_base = per_cpu_ptr(&timer_bases[b], cpu);
                 new_base = get_cpu_ptr(&timer_bases[b]);
                 /*
                  * The caller is globally serialized and nobody else
                  * takes two locks at once, deadlock is not possible.
                  */
                 raw_spin_lock_irq(&new_base->lock);
                 raw_spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
 
                 /*
                  * The current CPUs base clock might be stale. Update it
                  * before moving the timers over.
                  */
                 forward_timer_base(new_base);
 
                 WARN_ON_ONCE(old_base->running_timer);
                 old_base->running_timer = NULL;
 
                 for (i = 0; i < WHEEL_SIZE; i++)
                         migrate_timer_list(new_base, old_base->vectors + i);
 
                 raw_spin_unlock(&old_base->lock);
                 raw_spin_unlock_irq(&new_base->lock);
                 put_cpu_ptr(&timer_bases);
         }
         return 0;
 }
 
 #endif /* CONFIG_HOTPLUG_CPU */
 
 static void __init init_timer_cpu(int cpu)
 {
         struct timer_base *base;
         int i;
 
         for (i = 0; i < NR_BASES; i++) {
                 base = per_cpu_ptr(&timer_bases[i], cpu);
                 base->cpu = cpu;
                 raw_spin_lock_init(&base->lock);
                 base->clk = jiffies;
                 base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
                 timer_base_init_expiry_lock(base);
         }
 }
 
 static void __init init_timer_cpus(void)
 {
         int cpu;
 
         for_each_possible_cpu(cpu)
                 init_timer_cpu(cpu);
 }
 
 void __init init_timers(void)
 {
         init_timer_cpus();
         posix_cputimers_init_work();
         open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
 }
 
 /**
  * msleep - sleep safely even with waitqueue interruptions
  * @msecs: Time in milliseconds to sleep for
  */
 void msleep(unsigned int msecs)
 {
         unsigned long timeout = msecs_to_jiffies(msecs) + 1;
 
         while (timeout)
                 timeout = schedule_timeout_uninterruptible(timeout);
 }
 
 EXPORT_SYMBOL(msleep);
 
 /**
  * msleep_interruptible - sleep waiting for signals
  * @msecs: Time in milliseconds to sleep for
  */
 unsigned long msleep_interruptible(unsigned int msecs)
 {
         unsigned long timeout = msecs_to_jiffies(msecs) + 1;
 
         while (timeout && !signal_pending(current))
                 timeout = schedule_timeout_interruptible(timeout);
         return jiffies_to_msecs(timeout);
 }
 
 EXPORT_SYMBOL(msleep_interruptible);
 
 /**
  * usleep_range_state - Sleep for an approximate time in a given state
  * @min:        Minimum time in usecs to sleep
  * @max:        Maximum time in usecs to sleep
  * @state:      State of the current task that will be while sleeping
  *
  * In non-atomic context where the exact wakeup time is flexible, use
  * usleep_range_state() instead of udelay().  The sleep improves responsiveness
  * by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces
  * power usage by allowing hrtimers to take advantage of an already-
  * scheduled interrupt instead of scheduling a new one just for this sleep.
  */
 void __sched usleep_range_state(unsigned long min, unsigned long max,
                                 unsigned int state)
 {
         ktime_t exp = ktime_add_us(ktime_get(), min);
         u64 delta = (u64)(max - min) * NSEC_PER_USEC;
 
         for (;;) {
                 __set_current_state(state);
                 /* Do not return before the requested sleep time has elapsed */
                 if (!schedule_hrtimeout_range(&exp, delta, HRTIMER_MODE_ABS))
                         break;
         }
 }
 EXPORT_SYMBOL(usleep_range_state);
 

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.